1. Field of the Invention
The present invention relates to an intermediate frequency receiver, and more particularly, to an intermediate frequency receiver for digital multimedia broadcasting.
2. Description of the Related Art
A transmitting end for transmitting electromagnetic waves through the air in wireless communication is designed to satisfy the following conditions.
First, the transmitting end has to transmit the electromagnetic waves by using an optimal power so that-a receiving end can receive signals.
Second, when the transmitting end transmits the electromagnetic waves by using several channels, interferences between the channels have to be avoided.
The receiving end for selectively receiving electromagnetic waves in the air has to satisfy the following conditions.
First, the receiving end has to amplify weak signals in the air transmitted from the transmitting end, and in this case, ingress noise has to be avoided.
Second, when the receiving end receives signals through several channels, the receiving end has to receive only signals of a desired channel.
The wireless communication uses radio frequency (RF) signals as the signals transmitted from the transmitting end and received to the receiving end through the air. In the air, various types of noise and different types of frequency signals exist. Therefore, the electromagnetic waves are exposed to the noises, and strength of the signals is attenuated due to various factors in the air. In order to accurately select a desired frequency signal in this bad condition, an optimal receiver is required.
Examples of RF bands that are currently used include Band-II, Band-III, L-Band, DVB-H, ISDB-T, and so on. Therefore, various types of receivers that can receive signals in the various RF bands have been introduced.
FIG. 1 is a block diagram illustrating a conventional dual-band receiver.
Referring to FIG. 1, the conventional dual-band receiver 100 includes a filter 110, an input tuner 120, an amplifying unit 130, an RF tuner 140, a frequency mixer 150, an intermediate frequency (IF) tuner 160, and a local oscillator 170.
The filter 110 performs filtering on a signal in each of two bands received from an antenna. The input tuner 120 performs input tuning on the RF signal filtered by the filter 110 into a corresponding band. The amplifying unit 130 amplifies the RF signal tuned by the input tuner 120. The RF tuner 140 tunes the RF signal amplified by the amplifying unit 130 into a corresponding channel. The frequency mixer 150 mixes a frequency of the signal tuned by the RF tuner 140 with a frequency of an oscillating signal received from the local oscillator 170 to generate an IF signal. The IF tuner 160 tunes the IF signal obtained by the frequency mixer 150. The local oscillator 170 generates a local oscillating signal having a predetermined frequency.
Although not shown in the figure, since signals in a number of channels are received, in order to remove signals in channels which are not desired, a tracking filter has to be disposed at a front portion of the conventional receiver. When the tracking filter is disposed at the front portion of the receiver, in order to select a desired channel, a center frequency of the filter is changed whenever a corresponding channel is changed. Electrical characteristics of the receiver using the filter which changes the center frequency are worse than electrical characteristics of a receiver using a surface acoustic wave (SAW) filter having a fixed center frequency. In addition, there are differences between electrical characteristics of filters included in manufactured receivers, so that there is a problem in that the receivers have to be tuned by manual operation when mass-produced.
Since an apparatus capable of performing automatic gain control of the receiver is not produced, in order to perform gain control of the receiver, a number of external devices are needed for the receiver.
In addition, in order to receive a plurality of band signals, a receiver corresponding to a reception signal in each band has to be provided. In this case, an area and power consumed by a system are linearly increased.